The marine mollusk Aplysia has a relatively simple nervous system with large nerve cells, many of which can be individually identified and studied from animal to animal using cellular electrophysiological techniques. We have recently found that a group of neurosecretory cells which are known to release a hormone that induces egg laying behavior in this animal appears to alter the physiology of other neurons and synapses for an hour oR more following stimulation of the neurosecretory cells. From previous studies it is known that some of the affected neurons are involved in the neural control of the cardiovascular system. We are now studying these changes in detail to determine if a substance released from the neurosecretory cells acts hormonally to cause the long-lasting changes, to analyze the cellular mechanisms underlying them, and to determine if they serve to alter the neural control of the cardiovascular system during egg laying.